Elevators are passenger tools used frequently in daily life. In order to ensure safety of elevator applications, at present, according to the latest national technics regulations, when a rated speed of an elevator is less than 3.5 m/s, a compensating chain must be used; when the rated speed of the elevator is equal to or greater than 3.5 m/s, a compensating rope must be used, and the compensating rope must have a guide, i.e., a rope sheave; and when the rated speed of the elevator is equal to or greater than 4 m/s, an anti-rebound device must be additionally provided, that is, a tensioning device. When the elevator is in an emergency stop state, a cabin side or a counterweight side will continue to rush upward due to inertia, at this moment, the anti-rebound device may pull the compensating sheave to thereby pull an elevator cabin or a counterweight by the compensating rope so as to prevent dangerous situations such as loosening or bracketing of a steel wire rope and the like resulting from upward jumping due to the inertia. In order to improve this current situation, an idea is proposed by an expert in the art that a hydraulic device is used as the tensioning device to overcome the above-mentioned problems. However, a number of problems need to be considered before applying the idea to a practical occasion, for example, a problem of how to prevent oil leakage in an oil hydraulic circuit while a normal operation of the tensioning device is not influenced, and as another example, a problem of how to reduce time and cost for installation, transportation and later maintenance, and the like.